Answer:
I don't exactly know how to explain this in words but here are some emojis for your answer
How does the phrase "a million mosquitoes" affect the passage?
A. It implies that there is a large amount of mosquitoes in the yard.
“A million something” (in this case mosquitoes) is an hyperbolic figure of speech used to imply a large or excessive amount of something. Option B about Jack not being a reliable narrator could have been a possible answer but the passage is written using a third-person point of view, so Jack is not a narrator.
Are you able to give more detail on your question? So I can answer it please thank you!